The present invention relates to an apparatus and method of sending data over a telephone line and more particularly with sending utility usage information over a telephone line in response to receiving an interrogate signal from the telephone line.
The present invention is suited for sending utility usage data and can send utility usage information from virtually any utility monitoring device over a telephone line. The typical use of the present invention is in an automatic utility meter reading system in which the present invention is responsible for sending the utility usage information from at least one utility monitoring device over a telephone line in response to receiving an interrogate signal.
The automatic utility meter reading system for which the present invention is particularly suitable is described in co-pending application Ser. No. 543,372, filed Oct. 19, 1983 for a Centerpoint Automatic Meter Reading System. This meter reading system is generally located at a central telephone office where a multiplexor system, best described in co-pending application Ser. No. 544,110, filed Oct. 21, 1983 for A Multiplexor for An Automatic Utility Meter Reading System, sends a series of distinct interrogate signals over a plurality of telephone lines. Each of the telephone lines has connected to it at least one of the apparatus of the present invention. In response to receiving a particular distinct interrogate signal, each of the present apparatus then causes a utility monitoring device to deliver its utility usage information which is sent over the telephone line to the multiplexor. The multiplexor decodes and stores the received meter readings for subsequent retrieval and mass storage by a microcomputer. The apparatus of this invention may also be accessed from the telephone central office via the metallic test access port and the subscriber line by manual dialup of the subscriber number.
There have been systems for sending utility usage data over telephone lines. One such system can be found in U.S. Pat. No. Re. 26,311 to Dumont et al. This system uses the telephone companies leakage testing system to call up the individual meter installations. Once a meter installation is called up, it sends the meter information over the telephone line to a central telephone office. However, the Dumont invention requires the use of a telephone company's leakage testing system to be operable and such leakage testing system can change, requiring an additional large investment in new equipment configured to the new leakage testing system. As well, not all telephone companies have the same type of leakage testing equipment, so that numerous configurations of the meter reading system must be devised to fit the numerous types of leakage testing equipment.
The Dumont invention also requires a power supply, powered either from the power available at the meter installation site or from battery power, for each of its meter installations. Unlike the present invention, this requirement of a power supply makes the Dumont invention costly, more difficult to service, and makes the system prone to failures due to common power outages at the installation site.
Unlike the present invention, the Dumont invention requires a complex synchronous data output on the telephone line. The synchronous output requires that the meter installations send additional sync pulses over the telephone line. In the event that either the sync pulses or synchronous meter data is momentarily interrupted by even a short noise pulse, which is quite common on telephone lines, the meter data will be lost. In addition, lines must be read sequentially which greatly slows down the process.
Another system which has been used to send data over a telephone line is found in U.S. Pat. No. 3,922,490 to Pettis. The Pettis invention is a direct current system where several resistances are switched across tip and ring of the telephone line. The current drawn by the several different combinations of resistances connected to the telephone line are sensed at a central telephone office and any of several conditions are thus communicated. Typically, in the Pettis invention, the least significant digit pointer of a utility meter makes or breaks a switch depending on which half of its rotation the pointer is presently in. The making or breaking of the switch causes the resistance across the telephone line to change. This change is sensed at the central office and the cumulative count of changes in transition are totaled and the meter reading determined therefrom.
Of course, the Pettis invention, being a D.C. system, does not relate at all to the present invention which is an A.C. system for sending data over the telephone line. As well, the present invention sends an entire updated reading each time it is requested to do so; the Pettis invention requires that a first reading be known to the central telephone office and that all of the subsequent transitions of the least significant pointer be received without interruption for an accurate meter reading to be had. If there is any interruption in the receiving of the transitions greater than a typical transition period, the central office will have to send someone out to the installation site to read the proper meter reading to compensate for the lost transitions.
None of the above described inventions is responsive to alternating current interrogation signals, and none have a meter interface device which sends alternating current representations (while the telephone is ON-HOOK or OFF-HOOK) and is powered from the telephone line in either the ON-HOOK or OFF-HOOK state; and, powering a meter interface from the telephone line has some extremely important advantages which will be discussed later. As well, none of the above described inventions sends current utility usage information asychronously over the telephone line.